The invention relates to a control apparatus and a control method for controlling the set-up of calls between a first subscriber station and a second subscriber station which are connected to a telecommunication network. The invention also relates to a telecommunication system and a subscriber station comprising such a control apparatus.
Specifically the invention relates to telecommunication systems comprising a telecommunication network in which a CCBS (Completion Of Calls To Busy Subscriber) facility allows a calling subscriber station, which failed to set-up a call to a busy subscriber station, to be notified when the called busy subscriber station becomes idle again. When the notification takes place, the network offers automatic set-up (completion) of the call to the called subscriber station. Such a CCBS facility is used to take away the burden of successive re-dialing operations of the calling subscriber station to find out when the concerned second subscriber station becomes available again.
Without being limited thereto the present invention-relates to the usage of the CCBS facility in order to set-up data calls between a first and second subscriber station. However, the invention is also applicable to the setting up of speech calls between the subscriber stations.
Although the standardization for the CCBS facility is currently on the way within the ETSI standardizing committees in view of the GSM telecommunication system (Global System of Mobile Communication) for standardizing the set-up of speech calls between subscriber stations using such a CCBS facility, the invention is not limited to GSM and is likewise applicable to any telecommunication system where call set-up requests need to be transferred through a telecommunication network to a subscriber station.
The CCBS supplementary service has been already standardized by ETSI for a fixed network N-ISDN. It may be noted that it is possible that the CCBS system of GSM and the CCBS system of the fixed network N-ISDN cooperate. For example, one terminal can be a N-ISDN terminal connected to the fixed N-ISDN network and another terminal can be a GSM mobile station.
FIG. 6 shows an overview of a telecommunication system SYS including a telecommunication network NET and a plurality of subscriber stations SS1, SS2, SS3. The telecommunication network NET comprises an exchange means GMSC, MSC/VLR (A), MSC/VLR (B), HLR (A), HLR (B) for setting up calls between the subscriber stations and an operation state monitoring means CCBS, MON monitoring a respective operation state of the subscriber stations. Of course the network PLMN comprises other features (not shown) necessary for the operation of the network, for example the BSS (i.e. the GSM radio access network) including BSCs (i.e. base station controllers) and the BSs (i.e. the base stations). The BSS is provided between the mobile station MS and the mobile switching center MSC of the network PLMN. Although the BSS is not essential for operating the CCBS service, the CCBS service is exactly provided for the reason to save radio resources within the BSS which is the unit where resources will be occupied by the calls.
Although the operation state monitoring means CCBS, MON is illustrated as being incorporated in the telecommunication network NET, it may be located elsewhere in the telecommunication system, for example within the subscriber station itself or within an exchange means of other telecommunication-networks NETxe2x80x2 which may be connected to the telecommunication network NET. Within the present specification the operation state monitoring means CCBS, MON is for simplicity assumed to be located in the telecommunication network NET. The main function of the operation state monitoring means CCBS, MON is to provide a simple notification mechanism which informs a calling subscriber station that a destination (another subscriber station) previously being busy has become idle.
In FIG. 6 an example is illustrated where the telecommunication network NET is constituted by a public land mobile radio communication network PLMN and the subscriber stations are mobile stations MS (A), MS (B), MS (C). In this case the exchange means comprises (in addition to other means like the BSS explained above) mobile switching centres MSC, visitor location registers VLR (A), VLR (B), home location registers HLR (A), HLR (B) and a gateway mobile switching centre GMSC. MSC/VLR (A), HLR (A) and MSC/VLR (B), HLR (B) are respectively provided for the mobile stations MS (A), MS (B) between which a call set-up will be considered below, whilst it should be noted that similar means (not shown) are provided for the third mobile station MS (C).
The dotted line between the public land mobile radio communication network PLMN and the respective mobile-stations MS (A), MS (B), MS (C) indicate the radio interface. Furthermore, although not illustrated in FIG. 6, it should be noted that the telecommunication network NET can be constituted by a plurality of networks, for example a public and mobile radio network PLMN and a public switched telephone network PSTN, wherein one or more of the subscriber stations SS1, SS2, SS3 may be a telephone of a fixed network.
Although hereinafter with reference to FIGS. 7a, 7b the set-up of a call (the usual speech call) between the subscriber stations SS1, SS2, will be considered in view of the usage of the CCBS facility, it should be understood that the telecommunication network NET can also switch data calls which are for example issued by a subscriber station. SS3 which comprises a telephone equipment and a terminal equipment TE interconnected through a terminal-to-modem interface. In case the subscriber station SS3 is a mobile station MS (C) the telephone equipment is constituted by the mobile termination MT of type 2 (which means that the TDF (terminal adapter functions) are integrated).
It should be noted that FIG. 6 (and also FIG. 1 to be described below) only shows some common configurations of the subscriber stations including a mobile station e.g. consisting of a mobile termination MT and an interconnected terminal equipment TE. Here a mobile station MS can be regarded as the sum of terminal equipments handled by the user which can be either a mobile termination MT of type 0, a mobile termination of type 1 connected to an ISDN terminal, or a non-ISDN terminal connected to a mobile termination of type 2. The GSM standard GSM 04.02 Version 5.0.0: May 1996 defines the most common configurations used at the mobile stations. In the present specification, the term xe2x80x9cmobile stationxe2x80x9d (see e.g. the mobile station MS (C) in FIG. 6) comprises all such configurations without limitation.
The terminal equipment TE may be a computer, e.g. a laptop, on which the data application is implemented. The computer is connected to the mobile termination MT through the interface as is shown in FIG. 6. The data application implemented on the computer may for example be a FAX application, an electronic mail application, a file transfer application, an Internet Access Application, etc. The terminal equipment TE requests the mobile termination MT to issue a data call dependent on the implemented or executed data application. In. GSM such data-calls are typically transparent or non-transparent circuit-switched connections of a certain data rate which support the said-FAX, electronic mail, file transfer or Internet Access Applications. Depending on the functionalities of the mobile station and of the exchange of the telecommunication network NET, the data calls may in the future also be packet-orientated, wherein in the telecommunication network NET, PLMN a GPRS (General Packet Radio Service) may be provided.
Regarding the data calls, for a GSM mobile equipment the GSM standard specification 07.07 has standardized the AT command set to be used for setting up data calls. The AT command set is an interface to enable the terminal equipment TE (e.g. a laptop) to control the connected mobile termination MT to set-up a data call. The current standardization GSM 07.07 provides no possibility to allow the mobile termination MT to differentiate between the different applications running on the terminal equipment TE. This means that the mobile termination MT will not be able to contact the right application in the terminal equipment TE when it gets the indication from the network that a remote user has become free. Currently ETSI SMG4 suggests a solution to introduce a multiplexing on this interface and how to handle backwards compatibility.
Currently the ETSI standardization groups are working towards a standardization of the CCBS (Completion Of Calls To Busy Subscriber) supplementary service for GSM. CCBSxe2x80x94since it will become a standardxe2x80x94is one of the most-complex supplementary services. The CCBS recall handling within the mobile station is already for ordinary speech-calls (for example between the mobile stations MS (A), MS (B) one of the difficult key aspects to be implemented. The ETSI standardization has in principle agreed how to specify the recall handling for speech calls but has not really started the work for fax and data services.
Although the standardization process for the CCBS implementation is still on-going-and finalization can only be expected in early 1998, in principle the CCBS implementation is performed as shown in FIGS. 7a, 7b as is described in the GSM document 03.93. FIG. 7a shows a successful CCBS request where the called subscriber station B is in a busy state, when the call set-up request is issued by the first subscriber station A and where the subscriber station A is free (in an idle state) when the called subscriber station B becomes free (changes from a busy state to an idle state). The most important steps in the diagram in FIG. 7a will be explained hereinafter.
When the mobile station A (MS (A)) issues a call set-up request S1 this call set-up request is routed to the mobile switching centre MSC (B) (S2: Initial Address Message IAM; S3: Information Request; S4: Provide Roaming Number PRN; S5: Return Mobile Station Roaming Number MSRN; S6: Information Request Acknowledgment; S7: Initial Address Message) and the called subscriber station MS (B) is busy, a release message S8 is returned to the gateway MSC which routes the release message S9 to the mobile switching centre MSC of the mobile station MS (A). That is, if the second subscriber station is in a busy state, the operation state monitoring means CCBS, MON indicates to the first subscriber station MS (A) that the second subscriber station is in a busy state and that a CCBS activation is possible.
The first subscriber station may comprise an automatic recall means ARC (see FIG. 6) which provides a re-dial function to perform an automatic call set-up repetition as long as the call is not answered by the called subscriber station B. That is, without activating the CCBS facility the automatic recall means ARC will start again with step S1, i.e. it will repeat the call set-up request to the called subscriber station B andxe2x80x94if the second subscriber station is still busyxe2x80x94the call set-up will be again released by step S10.
The re-dial function (the automatic recall means) allows the execution of recalls within certain time intervals, e.g., every 60 seconds. The number of allowed re-dialings may be limited by a limitation means (as requested by law; for example applications are not allowed to support more than 20 re-dialings).
The reason why the number of re-attempts must be limited in the prior art is as follows. As is seen with steps S1-S10 in FIG. 7a, the automatic re-attempts to set-up a call in step S1 lead to the allocation of radio resources at the radio interface between the first subscriber station MS (A) and the exchange means MSC/VLR (A), HLR (A), GMSC, HLR (B), MSC (B). In addition, further resources within the radio access network (i.e. the BSS as explained above) are occupied. Essentially a signalling channel or even a traffic channel has to be set-up, cell changes of the called subscriber station might occur which need to be tracked, etc. Furthermore, terrestrial resources in the PLMN or a possibly connected external PSTN network need to be occupied. Thus, the many repetitions for setting up a call executed by an automatic recall means ARC use resources of the exchange means which are by most operators not charged, however prevent other users from making calls since the resources are occupied.
In order to reduce this problem, the calling subscriber station MS (A) may perform a CCBS activation in steps S11-S18, i.e. the user requests from the network the CCBS service for a specific call which has been rejected due to said called second subscriber station being in a busy state. After the CCBS request has been transferred to the home location register HLR (B) of the called subscriber station MS (B) in steps S11-S13, the CCBS facility (the operation state monitoring means) starts monitoring the second (busy) subscriber station in step S14 and an acknowledgment message CCBS request (Ack) is returned to the calling first subscriber station MS (A) through steps S15-S18.
After step S18 the operation state monitoring means CCBS, MON monitors the operation state of the called (busy) second subscriber station MS (B) and provides a CCBS recall function that consists of the notification that the busy second subscriber station has changed its operation state from a busy state to an idle state in steps S20-S23 if the release of the second subscriber station occurs in step S19. In step S22 a copy of the set-up message is provided and the CCBS recall message in step S23 requests the first subscriber station to perform a new call set-up (since the second subscriber station has become available for a call set-up). Instead of just requesting the first subscriber station to perform a re-dial (e.g. manually or via the automatic recall means ARC), the CCBS facility may also offer an automatic completion to the second subscriber station if this was requested by the first subscriber station initially when activating the CCBS facility in step S11 (of course this assumes that the first subscriber station is not busy at the time when the CCBS facility performs the call completion to the called second subscriber station which has become available again).
In response to the CCBS recall message, a call set-up request is transferred through steps S24-S32 whereafter an alert/connect message S35 is returned to the calling first subscriber station MS (A) through steps S33, S34 (ACM/ANM/CPG: acknowledge message/alert nominating message/call progress generation). The alert/connect message in step S35 indicates alerting of the second subscriber station that the call could be connected. In this connection, alert does not mean a failure but it is used for the providing of a ringing tone. If a call could be completed, then the HLR(B) is informed about this in step S37, the dialogue between the 2 HLRs is ended in step S38 and also the MSC(B) reports the successful call completion in step S39. In step S40 the CCBS facility stops its operation, i.e. the operation state monitoring means CCBS, MON stops the monitoring of the called second subscriber station, since a call was successfully set-up between the first and second subscriber stations.
As can be seen from FIG. 7a, steps S1-S10xe2x80x94when repeatedly executedxe2x80x94may be regarded as an automatic recall function {circle around (1)}. Steps S11-S18 may be regarded as the CCBS activation function {circle around (2)}. Steps S19-S23 relate to the CCBS recall function {circle around (3)} and steps S24-S40 relate to the call completion function {circle around (4)} after the second subscriber station has become free. The functions {circle around (2)}, {circle around (3)}, and {circle around (4)} are part of the usual CCBS completion of calls to a busy subscriber.
In FIG. 7b the steps S1-S23 correspond to those in FIG. 7a and will not be explained again. That is, the functions {circle around (1)}, {circle around (2)}, {circle around (3)} are the same. FIG. 7b differs from FIG. 7a in that the first subscriber station MS (A) is not in an idle state when the called subscriber station MS (B) becomes eventually available for a call set-up.
When for example a timer T10 expires in step S24xe2x80x2, this means that there has not been received a user reaction or the indication that the called subscriber station is now free, since the timer waits for such a reaction or indication in a predetermined time (by contrast, the busy-state of the called subscriber station is detected by a means in MSC (A) directly). Therefore, when the timer expires in step S24xe2x80x2, the monitoring of the second subscriber station and the provision of the CCBS facility for the second subscriber station is stopped in steps S27xe2x80x2, S26xe2x80x2 after a CCBS RUF acknowledgment message has been transferred in step S25xe2x80x2 (CCBS recall unified function).
Thereafter, in step S28, the monitoring process by the operation state monitoring means of the CCBS facility is started for the first subscriber station MS (A). Eventually in step S30xe2x80x2 the first subscriber station becomes available again and an event report message is transferred in step S31xe2x80x2. Thereafter, the CCBS facility is used again in step S32xe2x80x2 to start the monitoring process in steps S33xe2x80x2, S34xe2x80x2 again for the second subscriber station since it cannot be guaranteed that the second subscriber station is idle at exactly the same time when the first subscriber station becomes idle again in step S30xe2x80x2. In step S27xe2x80x2 the stop monitoring message is sent if there are only suspended requests in the waiting queue in case the CCBS facility handles several call set-up requests from several calling first subscriber stations at the same time. The start monitoring message in step S33xe2x80x2 is sent if the MSC (B) is not monitoring the called subscriber station (B) at the time when the calling first subscriber station MS (A) becomes idle.
As is seen from FIGS. 7a, 7b, the first subscriber station may activate a CCBS function within the network NET which partly reduces the problem of repeated call set-up requests occupying resources of the exchange means within the telecommunication network NET. That is, when a speech or data call is to be set up between the subscriber stations, the first subscriber station can wait until the CCBS recall message indicates that the second subscriber station has become available again. However, this procedure does not remedy the problem that a repeated re-dialxe2x80x94which despite the activation of the CCBS function may be issued by the first subscriber stationxe2x80x94will once again occupy resources in the telecommunication network.
Furthermore, the first subscriber station might ignore the possibility to use CCBS (which is most probably be charged for) and go on to use the re-dial functionality (which may not be charged and may only be limited by the number of available re-dials). Therefore, the problem with the re-dialings occupying resources in the network still inherently exist even for the speech call despite the provision of the CCBS function.
Considering that first of all the CCBS function would be standardized for the speech calls issued from the mobile equipment MT, this means that the re-dial functionality and the CCBS function will not immediately be available for handling the important data calls as was described with respect to the subscriber station SS3 in FIG. 6. That is, regarding the recall function and the CCBS activation function {circle around (3)}, {circle around (2)} in FIGS. 7a, 7b, it is expected that all data applications/fax applications have to be upgraded as soon as the standard has been established. This, in addition to the delayed standardization progress, contradicts an easy and fast introduction of the CCBS service in the field of data/fax services. For example, so far no attempt is known to upgrade the commands xe2x80x9cAT-transferxe2x80x9d and xe2x80x9cAT-dialxe2x80x9d (of the AT command set as was explained above with reference to FIG. 6) on the modem-fax interface between the connected terminal equipment (computer) and the mobile termination MT. That is, the ETSI standardization has in principle only agreed how to specify the recall handling for speech calls, but has as yet not really started to work on fax and data services.
Thus, independent of the fact, whether the call set-up request relates to a speech call or a data call, the occupying of resources within the telecommunication network NET, in particular within the radio interface(s) AI and the radio access network BSS of the telecommunication system by repetitive call set-up requests for the same call still presents a problem.
Therefore, the object of the present invention is
to provide a control apparatus, a control method, a telecommunication system as well as a subscriber station, which allow an optimal use of the resources of the telecommunication network when setting up calls between subscriber stations.
This object is solved by a control apparatus as defined in claims 1, 22. Furthermore, the object is solved by a control method as defined in claim 23 and claim 39. Furthermore, the object is solved by a telecommunication system as defined in claims 40, 41, 55. The object is also solved by a subscriber station as defined in claims 56, 60, 61.
Independent as to whether the call set-up request issued by the first subscriber station relates to a desired call for which a call set-up request has been issued beforexe2x80x94i.e. a repeated call set-up requestxe2x80x94or is a first call set-up request for which a previous call set-up request has not been issued before, a call set-up request blocking means blocks a transfer of the call set-up request issued by the first subscriber station to the exchange means of the telecommunication network, when it is activated by an activation means in response to said second subscriber stationxe2x80x94i.e. the called-subscriber stationxe2x80x94being in a busy state.
Since the exchange means in the telecommunication network is not occupied by call set-up requests which would eventually fail anyway (since the second subscriber station is busy) the resources, in particular in the BSS and the AI, are optimally used and are free for call set-up requests issued from other first subscriber stations to other second subscriber stations of the telecommunication system (or free for xe2x80x9cother types of callsxe2x80x9d of said first subscriber station e.g. to another second subscriber station).
The use of the call set-up request blocking means and the activation means is particularly advantageous if the handled call set-up request relates to a repeated call set-up request for example issued by an automatic recall means of the first subscriber station. A recall detection means will detect whether the call set-up request is a call set-up request issued by the automatic recall means of the first subscriber station. Preferably, in such a case, the control apparatus only blocks the user applications repeated re-dialings (repeated call set-up requests) as long as the CCBS service is activated and a remote user-free indication has not been received from the network. That is, there is not even a necessity that the full CCBS service is employed. It is only necessary that in view of the fact that some part of the CCBS service is employed which has a simple notification mechanism which informs the first subscriber station that the second subscriber station previously being busy has become idle. That is, only the operation state monitoring means must be provided in the telecommunication network since the call completion must not necessarily be performed through the CCBS recall and set-up function as explained above.
Preferably the first subscriber station comprises a telephone equipment and a terminal equipment connected thereto, wherein said call set-up request is issued by said telephone equipment triggered by said terminal equipment in order to set-up a data call between said terminal equipment and said second subscriber station. The inventive control apparatus can be arranged in the terminal equipment or in said telephone equipment. That is, by locating the inventive control apparatus anywhere (but not within the application) the applications themselfes and the interface to the application do not need to be updated. Thus, advantageously the terminal equipment, for example a computer, does not need to be updated once the standardization for the CCBS supplementary service for GSM has been finalized.
Preferably the activation means activates the call set-up request blocking means and the operation state monitoring means of the telecommunication network if the call set-up request issued by said first subscriber station is rejected by the telecommunication network, i.e. by its exchange means.
The activation of the call set-up request blocking means can be performed with the receipt of the first call set-up request or after a predetermined number of repetitive call set-up requests relating to the same call have been issued by the automatic recall means of the first subscriber station and have been rejected by the exchange means of the telecommunication network.
What is meant with xe2x80x9ccall set-up requestxe2x80x9d is e.g. the request coming from an application such as a dial (see FIG. 4) if e.g. the inventive control apparatus is located between the application and the MS core.
When the first subscriber station comprises an automatic recall means for repeating a call set-up request to the second subscriber station, the recall detection means can preferably detect that a call set-up request is a repeated call set-up request relating to the same call by comparing a set of call parameters contained in the call set-up request with sets of call parameters stored in a call parameter memory which stores call parameters for previous call set-up requests. When the call parameters of a received call set-up request and an entry in the call parameter memory match, it can be detected that the newly received call set-up request relates to a call for which a call set-up request has already previously been issued.
Furthermore, the recall detection means can preferably detect a time interval between successive call set-up requests issued by said first subscriber station to said second subscriber station and can detect that a call set-up request has been issued by said automatic recall means of said first subscriber station, if the detected time interval is within a predetermined time interval.
The time interval detection can be used together with the call parameter comparison, for example the control apparatus can be trained (e.g. by observation) in order to learn when an application uses the re-dial function by the automatic recall means. For example, if always a similar time interval is used to reach a certain destination with identical call parameters stored in the call parameter memory, then the control apparatus is trained to accept in the future such a time interval as an indicator for identifying recall occurrences, i.e. that a received call set-up request relates to a call for which a call set-up request has already been issued previously.
Once the recall detection means detects that a call set-up request is a repeated call set-up request (i.e. a re-dial) the activation means will activate the call set-up blocking means (such that the call is not transferred to the exchange means of the network) and a busy state indication can be sent back to the first subscriber station when the second subscriber station is in a busy state (i.e. cannot accept a call set-up).
Preferably, a delay means can be provided for delaying the activation of the call set-up request blocking means by the activation means and for delaying the sending of a busy state indication to the first subscriber station for a predetermined delay time interval. The advantage is that when the response xe2x80x9cbusy state indicationxe2x80x9d is sent back to the calling application (or the first subscriber station if the control means is located in the network) as late as possible, the first subscriber station""s call set-up request can be queued for some time in order to be available for a possibly arriving idle state indication of said second subscriber station from the network. According to another embodiment the delay means can also only delay the sending back of the busy state indication to the calling first subscriber station whilst the blocking is performed nonetheless.